<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        #outer{
            width: 300px;
            height: 300px;
            margin: auto;
            /* border: 1px solid red; */
            
            /* 设置边框的阴影部分 */
            box-shadow: 2px 2px 10px #ccc;

            /* 设置边角 
               width和height一致的情况,  50% - 圆形
            */
            /* border-radius: 10px; */
            border-radius: 50%;
        }
    </style>
</head>
<body>
    <div id="outer"></div>
</body>
</html>